The present invention is directed to aircraft electrical power systems and, more particularly, to a redundant electrical DC power generation system for aircraft.
All aircraft are required to have backup power systems. Previous DC power systems used starter generators as the normal means of powering electrical equipment with batteries serving as emergency backup power sources. Some systems used auxiliary power units (APUs) for engine starting and emergency power. Other systems use transmission, hydraulic or ram air driven generators for emergency power.
The aircraft industry has previously built power systems that have starter generators as a normal power source and a battery as a backup source. Most power systems use starter generators (one per engine). An electrical starter generator starts the aircraft engines. Once started, the engines cause power generation through the starter generators resulting in the provision of electrical power to busses through line contacts. A typical twin engine starter generator power system would consist of two starter generators, one per engine. A starter generator would be used for starting the first engine and for providing, for example, electrical power to the left hand busses. A second generator would be used for starting the second engine and providing power to the right hand busses. Power distribution is split up in this manner for the purpose of sharing the distribution load during normal operation, and for providing backup in the event of a failure of one of the generators. If, for example, the first generator were to fail, the power system would compensate by providing power to all buses through the remaining generator.
Relays create an electrical path between each side of the power system circuitry. Such a scenario, however, can overload the remaining generator, resulting in its failure as well. Most power systems, therefore, also include a battery backup for providing supplemental power to the electrical system if one or both of the generators fail. The battery feeds power to the emergency busses and the essential busses.
Assuming a scenario where one engine in a two engine configuration malfunctions, the drive for the associated generator would also be lost. If, for example, the first generator becomes inoperable, the second generator would then be responsible for powering the entire electrical system. Under these circumstances, the second generator can become overloaded. If it overheats or fails, the aircraft is left with mere battery power. This is an unfortunate situation because typically the battery would provide emergency power for a minimum of 30 minutes of operation for FAA (Federal Aviation Administration) regulated flight, or 60-90 minutes for CAA (Civil Aviation Authority in Great Britain) or JAA (Joint Aviation Authority in Europe) regulated flight.
IFR (Instrument Flight Rule) operations are typically met in the United States with a battery that operates for 30 minutes to back up power from the generators. In the scenario where a pilot loses both generators, the pilot must quickly find the nearest airport and land, otherwise all power will be lost resulting is a black cockpit, or worse in the case of xe2x80x9cfly by wirexe2x80x9d aircraft, a mechanically un-operational aircraft.
Failure of power generation systems can potentially cause loss of enough equipment on the aircraft that a pilot would not be able to maintain continued safe flight or landing. Continued electrical power is especially critical in xe2x80x9cfly by wirexe2x80x9d aircraft, where a lack of necessary redundancy and discontinued power generation in such aircraft can result in complete aircraft inoperability.
What is needed is a system that provides enough electrical power system separation and redundancy to maintain safe flight and landing of aircraft, regardless of partial system malfunction or loss.
In accordance with the present invention, a redundant aircraft DC power system is provided. The redundant DC electrical power system for aircraft comprises a primary power system including a transmission driven power generator, dedicated generator control unit and an isolated distribution network that further includes electrical busses for providing sufficient capacity to electrical loads on the aircraft. The DC electrical power system also provides an emergency power system including at least one engine driven starter generator with an associated controller unit and associated distribution network that is isolated from the primary power system. The emergency power system provides sufficient backup capacity to the aircraft electrical loads in the event that the primary power system fails.
In one embodiment, the power generation system includes at least three generators for providing normal and emergency DC power to an aircraft electrical system and components. The primary power system includes a transmission driven DC power generator, a dedicated generator control unit and a distribution network that includes busses for providing sufficient capacity to all electrical loads on the aircraft. The emergency power system includes two engine driven starter generators, each with an associated controller unit and associated distribution network for providing sufficient backup capacity to electrical loads assigned to each generator. Each starter generator system is sufficient to start its own engine and provide all emergency electrical loads assigned to it. An aircraft battery of sufficient capacity to start the engines and supply ground power prior to engine start up would complete the aircraft electrical power system. A battery, unlike prior systems, is not considered the emergency electrical power source for the aircraft when implementing in the present inventive system.
The primary and emergency power generation systems and their respective busses are isolated from each other when all generators are on line. This prevents ground or high voltage faults from affecting all of the equipment while a fault is being cleared.
The equipment busses are set up so that emergency busses have three power sources and three paths. The emergency busses contain equipment necessary for continued safe flight and landing. The essential and main power busses have two power sources and two paths. The nonessential bus has one power source.
The DC power system of the present invention provides electrical power to the fight controls, avionics, and electrical subsystem equipment without need for a heavy battery or inefficient backup system for emergency electrical power.